There are circumstances in which round wire, that is wire which has a circular cross-section, is preferred over wire which is not round. This preference may be due to the use of the wire in machines which can only use round wire and would be too expensive to alter for other wire, for example, welders. The preference for round wire may also be due to the desire for properties which do not vary depending on the direction of use. For example, flat wire will bend easier in one direction than another, whereas round wire bends the same in all directions.
Conventional round wire is typically formed by drawing a large piece of metal in tension through a die, stretching it to a smaller diameter. The metal being drawn must be ductile enough to undergo the large deformations involved in drawing or else it will break rather than stretch. Conventional wire may also be formed by casting wire from molten metal directly into its final shape. However, the casting of wire, for example, pouring molten metal directly into a groove on a spinning disk as is done in the prior art, requires metering the amount of liquid being poured through a nozzle to get a wire of continuous diameter. One such system is described in U.S. Pat. No. 3,710,842.
Unfortunately, some metals and alloys which are desirable as round wire are brittle, precluding them from being drawn into wire in the conventional way. Additionally, casting involves flow metering of the metal through a nozzle to avoid variations in the diameter of the wire, which is difficult to do successfully.
One method for forming wire which is brittle when solidified is to bring the molten metal into contact with a heat extracting, rotating drum to which rapidly solidified metal adheres and is drawn away from the liquid metal, forming a wire. However, wire formed by this rapid solidification method is usually rectangular in cross-section, not round. Two methods for forming wire in the above described manner are melt overflow and melt extraction. Maringer et al., in U.S. Pat. No. 3,838,185, and Hackman et al., in U.S. Pat. No. Re 33,327 which is a reissue of U.S. Pat. No. 4,813,472, describe the melt overflow and melt extraction methods.
Therefore, the need exists for means and methods by which round wire can be formed of brittle metals, and which do not require difficult flow metering.